//	Copyright (C) 2002 The Npgsql Development Team
//	npgsql-general@gborg.postgresql.org
//	http://gborg.postgresql.org/project/npgsql/projdisplay.php
//
// Permission to use, copy, modify, and distribute this software and its
// documentation for any purpose, without fee, and without a written
// agreement is hereby granted, provided that the above copyright notice
// and this paragraph and the following two paragraphs appear in all copies.
// 
// IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
// FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
// INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
// DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
// THE POSSIBILITY OF SUCH DAMAGE.
// 
// THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
// ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
// TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
//
//	ConnectorPool.cs
// ------------------------------------------------------------------
//	Status
//		0.00.0000 - 06/17/2002 - ulrich sprick - creation
//		          - 05/??/2004 - Glen Parker<glenebob@nwlink.com> rewritten using
//                               System.Queue.

using System;
using System.Collections.Generic;
using System.Data;
using System.Threading;
using System.Timers;
using Timer = System.Timers.Timer;

namespace Npgsql
{
	/// <summary>
	/// This class manages all connector objects, pooled AND non-pooled.
	/// </summary>
	internal class NpgsqlConnectorPool
	{
		/// <summary>
		/// A queue with an extra Int32 for keeping track of busy connections.
		/// </summary>
		private class ConnectorQueue : Queue<NpgsqlConnector>
		{
			/// <summary>
			/// The number of pooled Connectors that belong to this queue but
			/// are currently in use.
			/// </summary>
			public Int32 UseCount = 0;

			public Int32 ConnectionLifeTime;
			public Int32 InactiveTime = 0;
			public Int32 MinPoolSize;
		}

		/// <value>Unique static instance of the connector pool
		/// mamager.</value>
		internal static NpgsqlConnectorPool ConnectorPoolMgr = new NpgsqlConnectorPool();

		public NpgsqlConnectorPool()
		{
			PooledConnectors = new Dictionary<string, ConnectorQueue>();
			Timer = new Timer(1000);
			Timer.AutoReset = true;
			Timer.Elapsed += new ElapsedEventHandler(TimerElapsedHandler);
			Timer.Start();
		}


		~NpgsqlConnectorPool()
		{
			Timer.Stop();
		}

		private void TimerElapsedHandler(object sender, ElapsedEventArgs e)
		{
			NpgsqlConnector Connector;
			lock (this)
			{
				foreach (ConnectorQueue Queue in PooledConnectors.Values)
				{
					if (Queue.Count > 0)
					{
						if (Queue.Count + Queue.UseCount > Queue.MinPoolSize)
						{
							if (Queue.InactiveTime >= Queue.ConnectionLifeTime)
							{
								Int32 diff = Queue.Count + Queue.UseCount - Queue.MinPoolSize;
								Int32 toBeClosed = (diff + 1) / 2;
								toBeClosed = Math.Min(toBeClosed, Queue.Count);

								if (diff < 2)
								{
									diff = 2;
								}
								Queue.InactiveTime -= Queue.ConnectionLifeTime / (int)(Math.Log(diff) / Math.Log(2));
								for (Int32 i = 0; i < toBeClosed; ++i)
								{
									Connector = Queue.Dequeue();
									Connector.Close();
								}
							}
							else
							{
								Queue.InactiveTime++;
							}
						}
						else
						{
							Queue.InactiveTime = 0;
						}
					}
					else
					{
						Queue.InactiveTime = 0;
					}
				}
			}
		}


		/// <value>Map of index to unused pooled connectors, avaliable to the
		/// next RequestConnector() call.</value>
		/// <remarks>This hashmap will be indexed by connection string.
		/// This key will hold a list of queues of pooled connectors available to be used.</remarks>
		private readonly Dictionary<string, ConnectorQueue> PooledConnectors;

		/*/// <value>Map of shared connectors, avaliable to the
        /// next RequestConnector() call.</value>
        /// <remarks>This hashmap will be indexed by connection string.
        /// This key will hold a list of shared connectors available to be used.</remarks>
        // To be implemented
        //private Dictionary<?, ?> SharedConnectors;*/


		/// <value>Timer for tracking unused connections in pools.</value>
		// I used System.Timers.Timer because of bad experience with System.Threading.Timer
		// on Windows - it's going mad sometimes and don't respect interval was set.
		private readonly Timer Timer;

		/// <summary>
		/// Searches the shared and pooled connector lists for a
		/// matching connector object or creates a new one.
		/// </summary>
		/// <param name="Connection">The NpgsqlConnection that is requesting
		/// the connector. Its ConnectionString will be used to search the
		/// pool for available connectors.</param>
		/// <returns>A connector object.</returns>
		public NpgsqlConnector RequestConnector(NpgsqlConnection Connection)
		{
			NpgsqlConnector Connector;

			if (Connection.Pooling)
			{
				Connector = RequestPooledConnector(Connection);
			}
			else
			{
				Connector = GetNonPooledConnector(Connection);
			}

			return Connector;
		}

		/// <summary>
		/// Find a pooled connector.  Handle locking and timeout here.
		/// </summary>
		private NpgsqlConnector RequestPooledConnector(NpgsqlConnection Connection)
		{
			NpgsqlConnector Connector;
			Int32 timeoutMilliseconds = Connection.Timeout * 1000;

			lock (this)
			{
				Connector = RequestPooledConnectorInternal(Connection);
			}

			while (Connector == null && timeoutMilliseconds > 0)
			{
				Int32 ST = timeoutMilliseconds > 1000 ? 1000 : timeoutMilliseconds;

				Thread.Sleep(ST);
				timeoutMilliseconds -= ST;

				lock (this)
				{
					Connector = RequestPooledConnectorInternal(Connection);
				}
			}

			if (Connector == null)
			{
				if (Connection.Timeout > 0)
				{
					throw new Exception("Timeout while getting a connection from pool.");
				}
				else
				{
					throw new Exception("Connection pool exceeds maximum size.");
				}
			}

			return Connector;
		}

		/// <summary>
		/// Find a pooled connector.  Handle shared/non-shared here.
		/// </summary>
		private NpgsqlConnector RequestPooledConnectorInternal(NpgsqlConnection Connection)
		{
			NpgsqlConnector Connector = null;
			Boolean Shared = false;

			// If sharing were implemented, I suppose Shared would be set based
			// on some property on the Connection.

			if (Shared)
			{
				// Connection sharing? What's that?
				throw new NotImplementedException("Internal: Shared pooling not implemented");

			}
			Connector = GetPooledConnector(Connection);


			return Connector;
		}

		private delegate void CleanUpConnectorDel(NpgsqlConnection Connection, NpgsqlConnector Connector);

		private void CleanUpConnectorMethod(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			try
			{
				Connector.CurrentReader.Close();
				Connector.CurrentReader = null;
				ReleaseConnector(Connection, Connector);
			}
			catch
			{
			}
		}

		private void CleanUpConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			new CleanUpConnectorDel(CleanUpConnectorMethod).BeginInvoke(Connection, Connector, null, null);
		}

		/// <summary>
		/// Releases a connector, possibly back to the pool for future use.
		/// </summary>
		/// <remarks>
		/// Pooled connectors will be put back into the pool if there is room.
		/// Shared connectors should just have their use count decremented
		/// since they always stay in the shared pool.
		/// </remarks>
		/// <param name="Connector">The connector to release.</param>
		public void ReleaseConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			if (Connector.CurrentReader != null)
			{
				CleanUpConnector(Connection, Connector);
			}
			else if (Connector.Pooled)
			{
				ReleasePooledConnector(Connection, Connector);
			}
			else
			{
				UngetNonPooledConnector(Connection, Connector);
			}
		}

		/// <summary>
		/// Release a pooled connector.  Handle locking here.
		/// </summary>
		private void ReleasePooledConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			lock (this)
			{
				ReleasePooledConnectorInternal(Connection, Connector);
			}
		}

		/// <summary>
		/// Release a pooled connector.  Handle shared/non-shared here.
		/// </summary>
		private void ReleasePooledConnectorInternal(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			if (!Connector.Shared)
			{
				UngetPooledConnector(Connection, Connector);
			}
			else
			{
				// Connection sharing? What's that?
				throw new NotImplementedException("Internal: Shared pooling not implemented");
			}
		}

		/// <summary>
		/// Create a connector without any pooling functionality.
		/// </summary>
		private static NpgsqlConnector GetNonPooledConnector(NpgsqlConnection Connection)
		{
			NpgsqlConnector Connector;

			Connector = CreateConnector(Connection);

			Connector.CertificateSelectionCallback += Connection.CertificateSelectionCallbackDelegate;
			Connector.CertificateValidationCallback += Connection.CertificateValidationCallbackDelegate;
			Connector.PrivateKeySelectionCallback += Connection.PrivateKeySelectionCallbackDelegate;

			Connector.Open();

			return Connector;
		}

		/// <summary>
		/// Find an available pooled connector in the non-shared pool, or create
		/// a new one if none found.
		/// </summary>
		private NpgsqlConnector GetPooledConnector(NpgsqlConnection Connection)
		{
			ConnectorQueue Queue;
			NpgsqlConnector Connector = null;

			// Try to find a queue.
			if (!PooledConnectors.TryGetValue(Connection.ConnectionString, out Queue))
			{
				Queue = new ConnectorQueue();
				Queue.ConnectionLifeTime = Connection.ConnectionLifeTime;
				Queue.MinPoolSize = Connection.MinPoolSize;
				PooledConnectors[Connection.ConnectionString] = Queue;
			}

			// Fix queue use count. Use count may be dropped below zero if Queue was cleared and there were connections open.
			if (Queue.UseCount < 0)
			{
				Queue.UseCount = 0;
			}


			if (Queue.Count > 0)
			{
				// Found a queue with connectors.  Grab the top one.

				// Check if the connector is still valid.

				Connector = Queue.Dequeue();
				/*try
				{
					Connector.TestConnector();
					Connector.RequireReadyForQuery = true;
				}
				catch //This connector is broken!
				{
					try
					{
						Connector.Close();
					}
					catch
					{
						try
						{
							Connector.Stream.Close();
						}
						catch
						{
						}
					}
					return GetPooledConnector(Connection); //Try again
				}*/
				
				if (!Connector.IsValid())
				{
        				try
        					{
        						Connector.Close();
        					}
        					catch
        					{
        						try
        						{
        							Connector.Stream.Close();
        						}
        						catch
        						{
        						}
        					}
        					return GetPooledConnector(Connection); //Try again
        		    
    				}
				Queue.UseCount++;
			}
			else if (Queue.Count + Queue.UseCount < Connection.MaxPoolSize)
			{
				Connector = CreateConnector(Connection);

				Connector.CertificateSelectionCallback += Connection.CertificateSelectionCallbackDelegate;
				Connector.CertificateValidationCallback += Connection.CertificateValidationCallbackDelegate;
				Connector.PrivateKeySelectionCallback += Connection.PrivateKeySelectionCallbackDelegate;

				try
				{
					Connector.Open();
				}
				catch
				{
					try
					{
						Connector.Close();
					}
					catch
					{
					}

					throw;
				}


				Queue.UseCount++;
			}

			// Meet the MinPoolSize requirement if needed.
			if (Connection.MinPoolSize > 0)
			{
				while (Queue.Count + Queue.UseCount < Connection.MinPoolSize)
				{
					NpgsqlConnector Spare = CreateConnector(Connection);

					Spare.CertificateSelectionCallback += Connection.CertificateSelectionCallbackDelegate;
					Spare.CertificateValidationCallback += Connection.CertificateValidationCallbackDelegate;
					Spare.PrivateKeySelectionCallback += Connection.PrivateKeySelectionCallbackDelegate;

					Spare.Open();

					Spare.CertificateSelectionCallback -= Connection.CertificateSelectionCallbackDelegate;
					Spare.CertificateValidationCallback -= Connection.CertificateValidationCallbackDelegate;
					Spare.PrivateKeySelectionCallback -= Connection.PrivateKeySelectionCallbackDelegate;

					Queue.Enqueue(Spare);
				}
			}

			return Connector;
		}

		/*
				/// <summary>
				/// Find an available shared connector in the shared pool, or create
				/// a new one if none found.
				/// </summary>
				private NpgsqlConnector GetSharedConnector(NpgsqlConnection Connection)
				{
					// To be implemented

					return null;
				}
		*/

		private static NpgsqlConnector CreateConnector(NpgsqlConnection Connection)
		{
			return new NpgsqlConnector(Connection.ConnectionStringValues.Clone(), Connection.Pooling, false);
		}


		/// <summary>
		/// This method is only called when NpgsqlConnection.Dispose(false) is called which means a
		/// finalization. This also means, an NpgsqlConnection was leak. We clear pool count so that
		/// client doesn't end running out of connections from pool. When the connection is finalized, its underlying
		/// socket is closed.
		/// </summary>
		public void FixPoolCountBecauseOfConnectionDisposeFalse(NpgsqlConnection Connection)
		{
			ConnectorQueue Queue;

			// Prevent multithread access to connection pool count.
			lock (this)
			{
				// Try to find a queue.
                if (PooledConnectors.TryGetValue(Connection.ConnectionString, out Queue) && Queue != null)
				{
					Queue.UseCount--;
				}
			}
		}

		/// <summary>
		/// Close the connector.
		/// </summary>
		/// <param name="Connection"></param>
		/// <param name="Connector">Connector to release</param>
		private static void UngetNonPooledConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			Connector.CertificateSelectionCallback -= Connection.CertificateSelectionCallbackDelegate;
			Connector.CertificateValidationCallback -= Connection.CertificateValidationCallbackDelegate;
			Connector.PrivateKeySelectionCallback -= Connection.PrivateKeySelectionCallbackDelegate;

			if (Connector.Transaction != null)
			{
				Connector.Transaction.Cancel();
			}

			Connector.Close();
		}

		/// <summary>
		/// Put a pooled connector into the pool queue.
		/// </summary>
		/// <param name="Connector">Connector to pool</param>
		private void UngetPooledConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
		{
			ConnectorQueue Queue;

			// Find the queue.
			if (!PooledConnectors.TryGetValue(Connection.ConnectionString, out Queue) || Queue == null)
			{
				return; // Queue may be emptied by connection problems. See ClearPool below.
			}

			Connector.CertificateSelectionCallback -= Connection.CertificateSelectionCallbackDelegate;
			Connector.CertificateValidationCallback -= Connection.CertificateValidationCallbackDelegate;
			Connector.PrivateKeySelectionCallback -= Connection.PrivateKeySelectionCallbackDelegate;

			Queue.UseCount--;

			if (!Connector.IsInitialized)
			{
				if (Connector.Transaction != null)
				{
					Connector.Transaction.Cancel();
				}

				Connector.Close();
			}
			else
			{
				if (Connector.Transaction != null)
				{
					try
					{
						Connector.Transaction.Rollback();
					}
					catch
					{
						Connector.Close();
					}
				}
			}

			if (Connector.State == ConnectionState.Open &&
                (Thread.CurrentThread.ThreadState & (ThreadState.Aborted | ThreadState.AbortRequested)) == 0)
			{
				// Release all resources associated with this connector.
				Connector.ReleaseResources();

				Queue.Enqueue(Connector);
			}
		}

		/*
				/// <summary>
				/// Stop sharing a shared connector.
				/// </summary>
				/// <param name="Connector">Connector to unshare</param>
				private void UngetSharedConnector(NpgsqlConnection Connection, NpgsqlConnector Connector)
				{
					// To be implemented
				}
		*/

		private static void ClearQueue(ConnectorQueue Queue)
		{
			if (Queue == null)
			{
				return;
			}

			while (Queue.Count > 0)
			{
				NpgsqlConnector connector = Queue.Dequeue();

				try
				{
					connector.Close();
				}
				catch
				{
					// Maybe we should log something here to say we got an exception while closing connector?
				}
			}
		}


		internal void ClearPool(NpgsqlConnection Connection)
		{
			// Prevent multithread access to connection pool count.
			lock (this)
			{
                ConnectorQueue queue;
				// Try to find a queue.
                if (PooledConnectors.TryGetValue(Connection.ConnectionString, out queue))
                {
                    ClearQueue(queue);

                    PooledConnectors.Remove(Connection.ConnectionString);
                }
			}
		}
		
		
		internal void ClearAllPools()
		{
			lock (this)
			{
				foreach (ConnectorQueue Queue in PooledConnectors.Values)
				{
					ClearQueue(Queue);
				}
                                PooledConnectors.Clear();
			}
		}
	}
}
